1. Technical Field
Compositions comprising paper processing waste as a source of cellulosic fiber and inorganic material are disclosed which are useful in manufacturing acoustic ceiling tiles and acoustic panels using a water felting process. More particularly, acoustic tile compositions using paper processing waste as a primary source of cellulosic fiber and a primary source of inorganic material are discussed which provide faster drainage times thereby reducing raw material costs and increasing line speed.
2. Description of the Related Art
The water felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a well-known commercial process for manufacturing acoustic ceiling tiles. In this process, an aqueous slurry of component materials such as mineral wool, perlite, binder (such as starch, latex, or others known in the art), inorganic material and cellulosic fiber is deposited onto a moving foraminous support wire, such as a Fourdrinier or Oliver mat forming machine, for dewatering or drainage. The slurry may be first drained by gravity followed by vacuum suction to form a base mat. The wet base mat is then pressed to the desired thickness between rolls and the support wire to remove additional water. The pressed base mat is then dried in ovens before the dried material is cut to the desired dimensions. The surfaces of the cut material can be sanded and top and/or bottom coated to produce acoustic ceiling tiles and panels.
Mineral wool acoustic tiles are very porous which results in good sound absorption. Starch is typically used as a binder in mineral wool-based ceiling tiles. Mineral materials, such as high density expanded perlite, are also used to enhance sound absorbing properties and to provide strength to the otherwise lightweight tiles and panels. While the use of expanded perlite can require a high level of water to form a workable slurry, the use of high density perlite can alleviate this problem.
Inorganic materials, such as clay are used in ceiling tiles to impart fire resistance (as defined by ASTM Test No. E119) because the clay sinters during the fire endurance test. Various commercial clays such as kaolin, and bentonite, etc. can be used in ceiling tile fabrication. Gypsum is an excellent inorganic material because it also acts as a flocculent. Calcium carbonate is another useful inorganic material because it is inexpensive and can add hardness to the finished product. One problem associated with inorganic materials is their tendency to settle to the bottom of the base mat during tile formation (due to high specific gravity) which increases drainage time and reduces line speed and therefore increases manufacturing costs.
Typically, the cellulosic fiber for ceiling tiles is obtained from either hydropulped or hammer milled newsprint that is being recycled. Recycled fibers from old newsprint have a substantial cost associated with their use as the long fibers recaptured from old newsprint can be processed into finished paper products. Refined paper and wood fibers may also be used for ceiling tile fibers. One problem with all of these fiber sources for ceiling tile is cost. The cost of manufacturing ceiling tiles could be reduced if a fiber source and perhaps an inorganic material source could be found amongst various existing waste streams which would enable ceiling tile manufacturers to obtain fiber and inorganic material sources for free or at a very low cost.
Each year, the 112 kraft-process paper mills across the United States produce approximately 1.5 million tons of waste material from their energy and chemical recovery processes. This waste material known as “paper sludge” is a clay-like material consisting of clays, calcium carbonate, short fibers (i.e., too short for use in making paper products), other inorganic materials and water. Another source of paper sludge is paper recycling processes where waste paper is received and de-inked prior to recovery of the longer fibers. During the de-inking process fiber sludge is generated, which contains particles of ink, materials such as clays and calcium carbonate, water and fibers too short to be converted to a recycled finished paper product.
In the past, paper sludge has typically been sent to landfills. With landfill costs rising and the potential for ground water contamination from landfill operations, many environmentally conscious paper producers are trying to recover the energy from paper sludge.
However, the paper sludge includes at least two components used in the manufacture of acoustic ceiling tiles: cellulosic fibers and inorganic materials (clay, calcium carbonate, etc.) It would be beneficial if paper sludge could be converted to a feedstock for acoustic ceiling tile manufacturing as it would avoid the cost and environmental impact of landfill disposal of paper sludge. More importantly for ceiling tile manufacturers, the use of paper sludge as a raw material in ceiling tile formation could replace at least two costly raw materials—cellulosic fibers from hydropulped paper processing and inorganic material—with one inexpensive and readily available material in the form of paper sludge.